An operon in the bacterium Salmonella typhimurium has the following arrangement:

The promoter for this operon is contained within a TE. The H2 gene encodes a protein that is part of the bacterial flagellum. The rHl gene encodes a repressor protein that represses the HI gene, which is found at another location in the bacterial chromosome. The HI gene also encodes a flagellar protein. When the promoter is found in the arrangement shown here, the H2lrHl operon is turned on. This results in flagella that contain the H2 protein. The HI protein is not made because the rHl repressor prevents the transcription of the HI gene. At a frequency of approximately 1 in 10,000 (which is much higher than the spontaneous mutation rate), this strain of bacterium can "switch" its expression so that H2 is turned off and HI is turned on. Bacteria that have HI turned on and H2 turned off can also switch back to having H2 turned on and HI turned off. This switch also occurs at a frequency of about 1 in 10,000. Based on your understanding of transposons and recombination, explain how switching occurs in Salmonella typhimurium. Hint: Take a look at solved problem S2.

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DR IR IR DR promoter- H2 rHl